The present invention relates to a process for the automatic correction of the focusing of a microscope and to an apparatus for performing said process. A particular application of the invention is to the field of medical analysis, particularly when it is desired to count the blood cells.
In processes and apparatus for the automatic analysis of images given by a microscope, it is frequently necessary to correct during the analysis the focusing of said microscope. Thus, the thickness of the slides carrying the preparations to be analysed is not generally constant and the focusing effected for a particular zone of said slide may no longer be correct for a neighbouring zone. It is therefore necessary to correct the focusing during the displacement of the slide beneath the objective of the microscope. Even if the pre-analysis focusing can be performed manually by the operator, this is not the case for the corrective focusing during analysis which must preferably be rendered automatic if the full benefits of the automatic nature of the actual analysis is to be obtained.
Processes and apparatus are already known for the automatic correction of the focusing of a microscope. In general manner, these processes comprise performing an analysis of an image which the microscope gives to an object for a given focus control, and correcting said focus control to give the maximum contrast to the image. Such process and apparatus are described in DOS 2,500,714 filed on 9.1.1975 and U.S. Pat. 3,967,056 granted on 29.6.1976.
In said processes and apparatus two successive focus controls of the same image are compared by measuring the contrasts of the two images obtained. It is therefore necessary for memory storage means for the contrast measurements to be provided to enable such a comparison to take place. Moreover, correction can only take place when two image analyses have been performed. As a result said processes and apparatus are slow.